The present invention relates to a method of fabricating a MOS-type transistor having a LDD (Lightly Doped Drain and Source) structure and more particularly, to a method of fabricating a MOS-type transistor which has a gate electrode made of molybdenum.
FIG. 3 shows the structure of a conventional MOS-type transistor. This transistor is of a LDD structure and has a gate electrode made of molybdenum. 11 denotes a silicon substrate. 12 is a gate insulating layer. 13 is a gate electrode made of molybdenum. 14a and 14b are a low density diffusion layer and a high density diffusion layer, respectively and serve as a source/drain. 15 are side wall spacers.
In the prior art, the gate electrode 13 and the low density diffusion layer 14a (source/drain) overlap each other as shown in FIG. 3. This prevents high speed operation as the elements become complicated. Where the gate electrode is made of polysilicon, the polysilicon layer is oxidized under heat to form an oxidized layer around the gate electrode. The thickness of this oxidized layer may be adjusted so as to reduce the amount of overlapping. Molybdenum is however subject to sublimation during heat oxidation. It is quite difficult to form such an oxidized layer and thus, control the amount of overlapping between the gate electrode and source/drain in the event that the gate electrode is made of molybdenum.
It is an object of the present invention to provide a method of fabricating a MOS-type transistor having a LDD structure and including a gate electrode made of molybdenum, which can reduce the amount of overlapping between the gate electrode and source/drain.